The invention relates to a deflection unit for a cathode ray tube comprising at least a pair of saddle-shaped coils having coil portions, the coil portions comprising a front and a rear end portion and the deflection unit comprising a coil support, whose inner side is provided with the pair of coils.
The invention also relates to a method of manufacturing a saddle-shaped deflection coil having a front and a rear end portion.
Such a deflection unit is known from Research disclosure September 1991, page 715 in which a deflection unit having a line coil is described. The line coil is secured to the support after the position of the deflection coil is fixed, using a fixing member.
Although this known deflection unit yields satisfactory results in many instances i.e. an accurate position of the deflection coil on the support, less than satisfactory results have been achieved for designs in which the front end portion is of the lying flange type, i.e. following the general contour of the tube of the cathode.
It is an object of the invention to provide a deflection unit for a cathode ray tube in which, on average, the accuracy of positioning the deflection coil and support with respect to each other is improved.
To this end, the deflection unit in accordance with the invention is characterized in that each pair of deflection coils is provided at the front end portion, being of the lying front flange type, with two or more reference surfaces within a winding window, said surfaces extending in a plane (x-y) perpendicular to the longitudinal direction of the deflection unit (z-axis), and the support is provided with protrusions having corresponding surfaces.
In the deflection unit, the coil is provided with two or more surfaces within a winding window extending in the x-y plane. These surfaces define a reference plane for the coil, which plant is perpendicular to the longitudinal axis (z-axis). The coil support comprises corresponding protrusions also defining a pair of surfaces extending in the x-y plane. The matching surfaces enable the position of the coils in the z-direction to be accurately determined, reducing inaccuracy in this positioning and thus eliminating or at least reducing a source of error. The coil support is preferably provided with a hooking part at a part corresponding to the rear end portion of the inner window of the coil to secure the coil on the support. The hooking part fixes the coil while the protrusion in co-operation with the surfaces in the coil determines the z-position. The coil support is preferably also provided with means for pushing each coil against a longitudinal rib. In such an embodiment, the position of the coil is even better determined.